The celebrated crime novel "The Godfather" was authored by which writer?

Introduction / Context:
"The Godfather" is one of the most famous crime novels of the twentieth century and has inspired equally famous film adaptations. It appears frequently in exams under the books and authors section. The aim of this question is to recognise that the novel was written by Mario Puzo, and not by other well known writers or fictional characters listed among the options.

Given Data / Assumptions:

• The work named is the novel "The Godfather".
• The options include authors from very different periods and genres, and one fictional name.
• We assume the question refers to the original English novel published in the late twentieth century.
• Only one of the listed names is actually the author of this book.

Concept / Approach:
The concept here is basic literary awareness of modern bestsellers. Mario Puzo is the author of "The Godfather", which focuses on the Corleone crime family. The character Vito Corleone appears in the story but is not a real writer. John Milton and Harold Robbins are real authors of different eras and genres. Agatha Christie is famous for detective fiction but did not create this particular mafia centred narrative. The approach is to recall which name is tied to mafia fiction and to ignore both earlier classical authors and purely fictional entries.

Step-by-Step Solution:
Step 1: Recall that "The Godfather" is a novel about an Italian American mafia family and their internal and external conflicts. Step 2: Remember that Mario Puzo wrote this novel and later co wrote the screenplays for its film versions. Step 3: Look at John Milton, who is a seventeenth century English poet famous for "Paradise Lost", clearly belonging to a different era. Step 4: Notice that Vito Corleone is actually a character inside "The Godfather", the head of the family, not a real life author. Step 5: Consider Harold Robbins, a twentieth century novelist known for racy bestsellers, but he did not write "The Godfather". Step 6: Consider Agatha Christie, the queen of detective fiction, who created Hercule Poirot and Miss Marple; her stories differ significantly from mafia sagas. Step 7: Since only Mario Puzo matches the known authorship of this novel, we choose him as the correct answer.

Verification / Alternative Check:
Popular culture, film credits, and book covers all clearly attribute "The Godfather" to Mario Puzo. Exam guides also list this pairing as a standard item in books and authors tables. No credible source attributes this novel to any of the other names. Cross checking with such widely available references confirms that Mario Puzo is the only valid answer.

Why Other Options Are Wrong:
John Milton was a poet from a much earlier period and wrote epics like "Paradise Lost", not modern crime novels. Vito Corleone is a fictional mafia boss in "The Godfather", not an actual writer. Harold Robbins wrote popular novels of a different style and subject matter, but not this mafia saga. Agatha Christie focused on classic whodunit mysteries and is not associated with "The Godfather".

Common Pitfalls:
Some students may be tricked by the name Vito Corleone, because it is strongly associated with the story and may look like a plausible human name in a list of authors. Others might choose any famous novelist such as Agatha Christie or Harold Robbins without recalling the specific connection. The best way to avoid these mistakes is to firmly link "The Godfather – Mario Puzo" in memory and to remember that Vito Corleone exists only inside the fiction as a character.

Final Answer:
The novel "The Godfather" was authored by Mario Puzo.